Apparatus and method for horizontal subsea connection

ABSTRACT

Apparatus for substantially horizontal connection of a conduit to a subsea structure, the apparatus comprising a frame being connectable to and supportable by the subsea structure, the frame having docking means to allow horizontal connection means including a remotely operated vehicle and/or a toolskid to dock with the frame such that the frame is capable of bearing at least part of an operational load associated with the horizontal connection of the conduit to the subsea structure.

[0001] The present invention is an apparatus and method for horizontalsubsea connection of flexible or rigid flowlines and umbilicals orbundles (hereinafter referred to as conduits) to subsea structures.

[0002] One of the most complex tasks required to be undertaken by meansof diverless intervention is that of connecting conduits to subseastructures. Typically connection is achieved by fitting a terminationhead of a conduit to a connection hub of a subsea structure and thenperforming the connection with a subsea connection clamp.

[0003] Where the conduit is deployed to the seabed with an endtermination head at some time prior to connection, the technique iscalled On-seabed connection. In such cases, the conduit is pulled to thesubsea structure after deployment on the seabed and the termination headconnected to the subsea structure at a later date. This type ofconnection is used predominantly in the North Sea or other offshoreenvironments where the weather conditions are unpredictable. These typesof connections are usually compact and, as the connections arehorizontal, the size of the seabed structure is usually small.

[0004] Deployment of horizontal connections onto the seabed, rather thanonto the structure, involves some risk associated with the type ofseabed onto which the conduit is to be placed. Deployment on soft seabedwill result in sinkage of the conduit termination head, an increase inpull-in loads and reduced visibility. The operation of pulling thetermination across the seabed and into the connection position istypically performed by a toolskid mounted onto an ROV. The ROV providesthe electrical or hydraulic power, and buoyancy to allow it to supportthe toolskid and the termination head of the conduit. Thrusters areprovided on the ROV to manoeuvre it and the toolskid around. In generalthe toolskid functions to pull the termination head of the conduit tothe subsea structure and to connect the termination head to the subseastructure and is typically actuated by the ROV through a wetmateconnection.

[0005] The toolskid is designed to accommodate high pull-in andalignment loads. Consequently toolskids are required to be large enoughto cope with these mechanical loads as well as hydrostatic pressure.

[0006] On-seabed connection becomes very difficult in deep water. Whilstit is possible to use known, standard ROVs and toolskids up to a depthof 600 m, new designs of ROV and toolskid are required because thetoolskids must be larger and more powerful, because the hydrostaticpressure increases with depth. Furthermore, as depth increases,transmission becomes slower and more difficult, and the consequent delaymeans that the ROV is more difficult to control and higher pull-in andalignment loads are experienced.

[0007] Conduits may be connected to subsea structures by docking an ROVand toolskid onto the conduit termination head then flying thetermination head to the subsea structure along guide ropes, using awinch and the ROV thrusters. The ROV and toolskid then dock on thesubsea structure and connect the conduit to the structure.

[0008] U.S. Pat. No. 5,593,249 describes an ROV having a skid framemounted on it. The ROV is used to ‘fly’ the conduit from its position onthe seabed to the subsea structure. The skid frame houses a pair ofwinches which are used as well as the ROV thrusters to position the openend of a flowline at a suitable position for connection to the subseastructure. In such applications, a large load is borne by the ROV. Thismakes the apparatus disclosed in U.S. Pat. No. 5,593,249 unsuitable foruse in deep water, because of the large hydrostatic pressures andmechanical loads that would be borne by the ROV.

[0009] It is also known to use the ROV and the toolskid docked directlyon the subsea structure to perform the pull-in operation, using pull-inropes previously attached to the termination head by the conduit. Butduring the pull-in operation and the aligning operation, all the loadsare borne directly by the toolskid and the ROV which have to be designedin order to resist to these loads.

[0010] Another known conduit connection system (U.S. Pat. No. 5,501,549)consists of a housing with a pivotable frame which is used to manipulatethe end of the conduit between a slanting pulling position and a finalhorizontal connection point.

[0011] In yet another known conduit connection system, (GB2307288), anROV is used in conjunction with a lift line that extends from thesurface to support a skid and flowline. In this case, it is difficult tocontrol the position of the skid and conduit from the surface. Any heaveor pitch occurring at the surface will cause erratic movement of theflowline and may result in damage to the flowline and to the subseastructure.

[0012] It is an object of the present invention to obviate theseproblems and to allow horizontal connection of conduits to subseastructures in deep (>600 m) water.

[0013] In accordance with a first aspect of the present invention thereis provided an apparatus for substantially horizontal connection of aconduit to a subsea structure, the apparatus comprising a frame beingconnectable to and supportable by the subsea structure, the frame havingdocking means to allow horizontal connection means including a remotelyoperated vehicle and/or a toolskid to dock with the frame such that theframe is capable of bearing at least part of an operational loadassociated with the horizontal connection of the conduit to the subseastructure.

[0014] Preferably, the frame comprises a working area in which theconduit is connected to the subsea structure located, in use, adjacentto a connection point of the subsea structure and a handling areaadjacent to the working area which, in use provides access to the subseastructure.

[0015] Preferably, the frame is provided with a latch, the latch beingconnectable to the conduit to allow the conduit to be supported by theframe in a position adjacent to the frame.

[0016] Preferably, the frame further comprises docking means connectableto the subsea structure.

[0017] Preferably, the docking means comprises a sleeve adapted toco-operate with a guide pin located on the sub-sea structure.

[0018] Optionally, the frame is permanently attached to the subseastructure.

[0019] Preferably, the toolskid comprises a pull-in module and/or astroke-in module.

[0020] In accordance with a second aspect of the present invention thereis provided a method of connecting a conduit arranged substantiallyhorizontally and located on or near the seabed to a subsea structure,the method comprising the steps of pulling the conduit towards thesubsea structure, aligning the conduit with a conduit connection pointlocated on the subsea structure and connecting the conduit to theconduit connection point, wherein a frame capable of bearing at leastsome of the mechanical load associated with the steps required toperform the connection of the conduit to the subsea structure isconnected to and supported by the subsea structure before pulling theconduit.

[0021] Preferably, the step of pulling the conduit towards the subseastructure is performed by a pull-in module, removeably attached to theframe.

[0022] Preferably, the conduit is capable of being suspended from theframe for a predetermined period of time before connection to the subseastructure.

[0023] Preferably, the step of aligning the conduit with a conduitconnection point is performed by the pull-in module.

[0024] Optionally, the step of aligning the conduit with a conduitconnection point is performed by a stroke-in module.

[0025] Embodiments of the present invention will now be described by wayof example, only with reference to the accompanying drawings of which:

[0026]FIGS. 1a and 1 b are perspective views of a docking frame inaccordance with the present invention, FIG. 1c is a side view of thedocking frame of FIGS. 1a and 1 b and FIG. 1d is a plan view of thedocking frame of FIGS. 1a and 1 b;

[0027]FIGS. 2a to 2 h show the use of the docking frame to install aseabed deployed horizontal connection in accordance with the method ofthe present invention;

[0028]FIG. 3 is a perspective view of a single frame in accordance withthe invention; and

[0029]FIG. 4 is a side view of an articulated frame in accordance withthe present invention.

[0030]FIGS. 5a to 5 d illustrate another embodiment of the docking frameaccording to the invention.

[0031]FIGS. 5a and 5 b are plan views of the frame and the terminationend of the conduit during alignment operations. FIG. 5c is a side viewof an alignment operation. FIG. 5d is a plan view after the stroke-in ofthe conduit, i.e. after the conduit has been moved into its finalposition, ready for clamping to the subsea structure.

[0032] The apparatus and method of the present invention are designed toprovide a way of performing substantially horizontal on-seabedconnection of a conduit such as a rigid or flexible pipeline, anumbilical, a bundle of lines or any other subsea conduit. In order to doso, a frame has been designed for connection to the subsea structure,such that the frame is capable of bearing some or all of the loadsassociated with horizontal on-seabed connection that were previouslyborne mostly by the ROV and toolskid. In particular, the frame of thepresent invention is capable of bearing at least 75% of these loads.

[0033]FIGS. 1a to 1 d show a docking frame 5 in accordance with thepresent invention attached to a subsea structure 1.

[0034] In this example, the frame 5 is attached to a subsea porchstructure having two inboard hubs 2 (see FIG. 1c) to which- pipelinescan be attached.

[0035]FIG. 1a is a perspective view with the docking frame 5 shown indark shading and the subsea structure 1 shown in light shading. Detailsof the docking frame 5 will be described with reference to FIGS. 1b, 1 cand 1 d.

[0036]FIG. 1b shows the docking frame 5 having a work area 8 which is,in this example, used to facilitate clamp operations such as sealreplacement, seal area inspection and cleaning, clamp opening andclosing, external seal testing and clamp removal and replacement.Handling area 9 is used to provide access to the area on the subseaporch 1 where the termination head of the pipe will be handled.

[0037] Typically, a pull-in-Module (PIM) (see FIGS. 2a to 2 e) containedon a toolskid is used to pull the termination head from the seabed tothe structure. The PIM is provided with at least one winch 21 forpulling the termination head from the seabed to the seabed structureusing a rope 22 previously connected to the termination head. Once thispulling is done, the termination head is then guided and aligned to it'sworking position illustrated in FIG. 2f. This alignment can be performedusing guiding end aligning means situated on the frame 5 and actuated bythe PIM 20. These means may use a handling frame movable along part ofthe docking frame 5 and a hang off latch 26 and a rear cylinder 25 forjoining the termination head to the handling, frame with a firstvertical orientation (see FIG. 2c).

[0038] In an alternative embodiment, the horizontal and verticalorientation of the termination head is adjustable using only the PIM,which can rotate the termination head and move it axially into itsworking position. When the termination head has been pulled to theframe, it can be handled either by a specific arrangement on the frameor by the PIM of the toolskid to perform the alignment of the conduit toit's working position. This can be done because most of the mechanicalload and hydrostatic load is borne by the frame. A stroke-in-module(SIM) is then used to provide an axial stroke of the termination head toa connection clamp and is used to connect the termination head and theconnection hub.

[0039]FIGS. 5a to 5 d show in detail the guiding and aligning means andthe handling means of one embodiment of a docking frame according to thepresent invention. The frame 205 comprises two pivotable outer slideboxes (206 a and 206 b) for accommodating angular displacement and afront section 209. The slide boxes are pivotable on front section 209.The ROV will dock on front section 209. Cylinders are provided whichwill control the stroke-in distance, the lateral linear displacement andthe angular displacement of the outer slide boxes and ensure thealignment of the conduit in the horizontal plane and a favourableposition of the handling frame as illustrated in FIGS. 5a and 5 b. Theouter slide boxes support a conduit handling swivelling frame 207 whichhandles the termination end of the conduit using a clamp 211. A swivelconnection 208 with control cylinders 210 allows a pivotable movementbetween the handling frame and each outer slide box and ensures thealignment in the vertical plane as illustrated in FIG. 5c.

[0040] Referring to the drawings, interfaces 14 (see FIG. 1b) areincorporated in the frame 5 to enable docking and operation of an ROVand toolskids. The interfaces 14 of the frame will co-operate withdocking pins (not shown) of the toolskid. The PIM 20 (FIG. 2a) of thetoolskid can be designed with a winch 21 situated at the bottom of thetoolskid frame directly on the docking pins. Therefore, the load fromthe winch 21 would be transferred through interfaces to the frame andthe load path through the toolskid frame structure would be minimal. Theframe will then accommodate all the bending moment caused by the winch21 pull-in. In a preferred embodiment, the winch is pulling the rope 22directly without any other diverting means situated in the toolskid.

[0041] The docking frame 5 can be installed permanently on the subseastructure. But preferentially, the docking frame is a separatelydeployed unit. It can be removably connected to the subsea structure forthat, FIG. 3 shows an alternative embodiment of the frame 105 in which asingle docking frame 5 is removably connected to the subsea structure 1.In this example, the frame contains a docking sleeve or funnel 106 whichis connectable to a guide pin 107 located upon the subsea structure. Theguide pin 107 has a frusto-conical end 108 which makes it easier for thedocking sleeve to connect with the guide pin.

[0042] The guide pin 107 is also provided with pins 109 which co-operatewith slots in the side of the docking sleeve 106 to ensure the correctorientation of the frame 105 with respect to the subsea structure. Thedocking frame 105 may be deployed from the surface on a centralisedguide wire extending through the sleeve 106 for engagement with theguide pin 107 or it can be deployed on the seabed and installed laterusing an ROV.

[0043]FIG. 1b shows the frame 5 located on a subsea structure above twoconnection points which are located below the central actuation means 12(see FIG. 1d) of the connection clamp 3.

[0044] Each connection point is provided with a clamp 3 that contains acentral actuation mechanism 12 and a horizontal leadscrew which allowsfor a very narrow clamp width of the subsea connection clamp 3. Thisfeature further minimises the distance between pipe centres onceconnected to the subsea structure.

[0045] In addition, the clamp 3 may be replaced in-situ by unlockingdocking pins 13 (FIG. 1c), axially retracting the clamp until it clearsthe inboard hub 2 and then vertically moving the clamp through workingarea 8.

[0046] The method used to connect an on-seabed conduit will now bedescribed with reference to FIGS. 2a-2 h. The method and apparatus ofthe present invention utilise known ROV and toolskid designs. The firstmain toolskid component is the pull-in module (PIM) 20 which acts topull the termination head from the seabed to a hang-off position on thedocking frame. The PIM 20 may also house the handling mechanisms foraligning and orientating the termination into the working position. Thesecond main toolskid component is the stroke-in module (SIM) 19 (seeFIGS. 2g and 2 h) which houses tooling to enable hub preparationoperations and clamp closing operations. The SIM is also used for finalstroking and alignment of the termination head.

[0047] The procedure for manoeuvring the termination head to the seabedstructure is explained with reference to FIGS. 2a to 2 h.

[0048]FIG. 2a shows a termination head 4 of a conduit, in this case aflowline, deployed onto the seabed 100. Also shown is the docking frame5 which is mounted onto the subsea porch structure 1. The docking frame5 may be permanently mounted to the porch structure 1 or it could beretrievably mounted thereon. The ROV 121 is shown with a toolskidcontaining a PIM 20.

[0049] In FIG. 2b, the ROV 121 with PIM 20 has been landed on thedocking frame 5 and engaged on the interfaces 14. Previously a pull-inrope 27 on Winch 21 has been deployed by the ROV 121, and the ropeanchor 22 is attached to termination head latch point 23. It will beappreciated that more than one pull-in rope may be used.

[0050] In FIG. 2c, winch 21 then pulls the termination head 4 across theseabed and up to the docking frame 5. Once the termination head 4 is inclose proximity to the underside of the docking frame 5, hang-off latch26 is engaged. This hang-off latch 26 may be provided on an handlingframe of the docking frame 5. Thereafter, the termination head 4 isattached to the docking frame 5. This completes the pull-in of thetermination head 4 from the seabed to the docking frame 5.

[0051] The next stage is to align the termination head 4 and to move itinto the working position. It can be performed either directly by thePIM 20 or by guiding and aligning means provided on the frame 5 andactuated by the PIM 20.

[0052]FIG. 2c, shows the PIM docked on to the docking frame. The rearcylinder 25 is deployed to be attached onto reaction ring 24. The rearcylinder 25 is then energised to lift the rear of the termination head 4to be in position at the correct height and in primary axial alignmentwith the connection point of the subsea porch structure 1.

[0053] It is preferred that this alignment is done horizontally,although it can be done at an angle to the horizontal depending upon theconfiguration of the subsea connection point.

[0054]FIG. 2d shows the termination head 4 being actuated forward intothe working position by a handling unit 28 mounted within the PIMtoolskid 20. The handling unit 28 actuates a handling frame 10 and thehang-off latch 26. In this example, the handling frame consists of atrolley that is moveable along the docking frame towards and away fromthe subsea structure.

[0055] Alternatively, the PIM 20 can provide the functionality of thehandling unit 28 and handling frame. With the termination head 4 held onthe handling frame and the hang-off latch 26, the rear cylinder can bereleased. The handling frame and it's aligning means can then act toprovide secondary alignment of the termination head 4 with respect tothe connection clamp 3 and also to orientate the termination head 4 ifrequired.

[0056]FIG. 2e shows the termination head being structurally clamped tothe docking frame by the handling frame after the correct workingposition and orientation have been achieved. In this position thetermination head 4 is axially aligned with the connection clamp 3 andseparated by a distance of about 600 mm. The PIM toolskid 20 may then beundocked. FIG. 2f shows the docking frames without the ROV and PIMtoolskid 20.

[0057] The ROV fitted with SIM Toolskid 19 is then docked onto theinterfaces 14 on top of the docking frame 5, The SIM 19 is used toperform the following tasks:

[0058] Pressure Cap Removal;

[0059] Debris Cap Removal;

[0060] Seal removal/replacement; and

[0061] Seal Area Inspection and Cleaning.

[0062] Once the hubs have been prepared, the SIM 19 is used to strokethe termination head axially 600 mm to mate with the inboard hub flange2. The clamp 3 is then closed using the actuation mechanism 12. Anexternal seal test may be made to prove the connection integrity. Thisprocess could be reversed for seal replacement operations in the eventof a leaking connection.

[0063] It is envisaged that the configuration of the toolskid will bedependant on the technical specification required for a givenapplication. The distribution of tasks performed by each unit may alsochange. The PIM, for example, may be used only to pull the terminationinto the working position. The SIM would therefore have to perform allthe subsequent tasks. The toolskid may contain both PIM and SIM modulesthat pull-in and stroke-in operations can be carried out when the ROVand toolskid are docked on the frame. For example, the termination headwill be pulled in to its working position and thereafter, the finalstroke-in operation will be performed.

[0064] Alternatively, the pull-in and stroke-in operations can beperformed by PIM and SIM components mounted in separate toolskids. Thisallows the stroke-in of a first connection to be performedsimultaneously with the pull-in of a second connection performed using asecond ROV.

[0065] The configuration of the tooling modules may also change. Thetoolskid could be deployed from the surface while attached to the ROV.Alternatively, the toolskid could be deployed to the seabed in a basket,the ROV would then mate to the toolskid subsea.

[0066] The docking frame 5 can be deployed separately from the subseastructure and then connected to the subsea structure. This isparticularly appropriate where there are size or weight limitations thatpreclude deployment of the frame and subsea structure together. Or thedocking frame could be deployed using an ROV to push the frame into thecorrect position for docking.

[0067] Alternatively, the docking frame could be installed by deployingthe docking frame to the seabed in a basket from where it can be pickedup by an ROV and installed on a seabed structure. In this caseadditional ROV Buoyancy may be required to enable the ROV to lift theframe or on the frame itself. In addition, smaller guide pins may beused where the frame is installed by ROV.

[0068] Another option would be for the toolskid to be provided withcontrol and propulsion systems to enable it to operate as an ROV. Thiswould provide benefits in terms of size and weight of the units andresult in more efficient and speedy subsea operations.

[0069] Advantageously, by transferring most of the operational loadsfrom the ROV and the toolskid to the frame, it is possible to usestandard ROVs and toolskids for deepwater conduit connection and it ispossible to reduce the size of ROV and toolskid used for deep waterapplications.

[0070]FIG. 4 shows an articulated docking frame 51 having a joint 53that allows the end of the frame to be articulated. This arrangementallows the docking frame 51 to be deployed through a moon pool orsimilar structure where the fully extended docking frame 51 is longerthan the moon pool. Articulation allows the docking frame to be extendedonce it has cleared the area of the moon pool, usually on the sea bed.

[0071] Improvements and modifications may be incorporated herein withoutdeviating from the scope of the invention.

1. Apparatus for substantially horizontal connection of a conduit to asubsea structure, the apparatus comprising a frame being connectable toand supportable by the subsea structure, the frame having docking meansto allow horizontal connection means including a remotely operatedvehicle and/or a toolskid to dock with the frame such that the frame iscapable of bearing at least part of an operational load associated withthe horizontal connection of the conduit to the subsea structure. 2.Apparatus as claimed in claim 1 wherein at least 75% of the operationalload is borne by the frame.
 3. Apparatus as claimed in claim 1 whereinthe frame is provided with interfaces that can be fitted with dockingpins for connecting the toolskid and/or ROV to the frame.
 4. Apparatusas claimed in claim 3 wherein the toolskid contains a pull-in modulehaving a winch being situated adjacent to said docking pins.
 5. Anapparatus as claimed in claim 1 wherein the frame comprises a workingarea located adjacent to a connection point of the subsea structurewhere, in use, the conduit is connected to the subsea structure and ahandling area adjacent to the working area which, in use provides accessto the subsea structure.
 6. An apparatus as claimed in claim 1 whereinthe frame comprises guiding an aligning means to align and move theconduit to a working position.
 7. An apparatus as claimed in claim 1wherein the frame comprises a handling frame to support the conduit in aposition adjacent to the frame.
 8. An apparatus as claimed in claim 1wherein the frame further comprises docking means connectable to thesubsea structure.
 9. An apparatus as claimed in claim 8 wherein thedocking means comprises a sleeve adapted to cooperate with a guide pinlocated on the sub-sea structure.
 10. An apparatus as claimed in claim 1wherein the frame is permanently attached to the subsea structure.
 11. Amethod of moving a conduit arranged substantially horizontally andlocated on or near the seabed, to a subsea structure, the methodcomprising the step of connecting an ROV and/or toolskid to the conduit,docking the ROV and/or toolskid on a frame and pulling the conduit tothe subsea structure using the ROV and/or toolskid, the frame beingconnected to and supported by the subsea structure, wherein the framebears at least some of the mechanical load associated with connectingthe conduit to the subsea structure.
 12. A method as claimed in claim 11further comprising the step of aligning the conduit with a conduitconnection point located on the subsea structure and guiding the conduitto a working position.
 13. A method as claimed in claim 12 furthercomprising the step of moving the conduit from it's working position andconnecting the conduit to a conduit connection point located on thesubsea structure.
 14. A method as claimed in claim 11 wherein the stepsof said claims are performed by a pull in module.
 15. A method asclaimed in claim 13 wherein the step of connecting point is performed bya stroke-in-module.
 16. A method as claimed in claim 1 furthercomprising the step of suspending the conduit from the frame for apredetermined period of time before connection to the subsea structure.